INTRODUCTION:

Valsartan is chemically N-(1-Oxopentyl)-N-[[2'-(1H-tetrazol-5-yl) [1, 1'-biphenyl]-4-yl] methyl]-L-valine(Figure 1). Valsartan is potent Angiotensin II receptor blocker. It is mainly used as anti-hypertensive drug. It is used for treatment of high blood pressure, of congestive heart failure (CHF), and post-myocardial infarction (MI). By blocking the action of angiotensin, valsartan dilates blood vessels and reduces blood pressure^1-2.

Figure 1: Chemical structure of valsartan

From the literature survey, it was found that valsartan was estimated by analytical methods such as Spectrophotometry^3-9, HPLC^10-13 in single form or combination with other drugs. The objective of this study was to develop and validate a simple, precise and accurate spectrophotometric method for the estimation of valsartan in pharmaceutical dosage form as per ICH guidelines.

MATERIALS AND METHODS:

Instruments and reagents:

Agilent Cary UV -60 Spectrophotometer with 1cm matched Quartz cells were used for the estimation. Ultrasonicator (ANM -USC 100) and electronic balance (Infra 201 LEC) used for the experiment. Valsartan was obtained as a gift sample from Ranbaxy laboratories, Gurgaon. Two brands of valsartan tablets manufactured by Torrent pharmaceuticals (Valzaar) and Novartis (Diovan) were procured from local pharmacy. All the reagents were of analytical grade. Double distilled water was used throughout the experiment.

Selection of solvent:

The solubility of Valsartan is determined in variety of solvents as per pharmacopeia standard. Solubility test was carried out in different solvents like distilled water, methanol, ethanol, 0.1N sodium hydroxide. From the solubility studies it was found that valsartan is soluble in distilled water, methanol and 0.1N sodium hydroxide. In this study methanol and distilled water (50:50) were selected as solvent.

Preparation of Standard Stock Solution:

An accurately weighed quantity of 50mg was taken in a 50ml volumetric flask. 10ml of methanol was added to it. Then 20ml of solvent was added and sonicated for 15min. Then the volume was adjusted with solvent to get the concentration of 1000ug/ml. From this 10ml was taken into a 100ml volumetric flask and 80ml of solvent was added to it. This was sonicated for 10min and volume was diluted upto the mark with solvent to get a concentration of 100ug/ml.

Determination of λ_max:

The standard solution of valsartan (10ug/ml) was scanned in UV region (200-400nm) and the spectrum was recorded. Solvent was used as blank. It was seen that at 248.21nm maximum absorbance was found, shown in figure 2. Therefore that 248.21nm was selected for this study.

Figure 2: Absorbance spectra of valsartan

METHOD VALIDATION:¹⁴

The objective of method validation is to demonstrate that the method is suitable for its intended purpose. The method was validated for linearity, precision, accuracy, robustness, ruggedness, LOD, LOQ, and specificity as per ICH guidelines.

Linearity:

From the standard stock solution, the various dilutions in the concentration of 2, 4, 6, 8, 10, 12, 14. 16, 18, 20 were prepared. The solutions were scanned at 248.21nm and the absorbance was recorded, given in table 1. From this calibration curve was obtained by plotting absorbance versus concentration of valsartan and the linearity graph was represented in figure 3. The correlation coefficient was found to be 0.999.

Figure 3: Calibration curve of valsartan

Table 1: Linearity parameter for valsartan

Concentration(µg\ml)	Absorbance(nm)
2	0.2064
4	0.4128
6	0.6192
8	0.8256
10	1.0236
12	1.2546
14	1.4448
16	1.6512
18	1.8576
20	2.0151

Precision

Repeatibility of the method was checked by scanning 10 µg/ml solution for 6 times. Intra-day precision was determined by checking the absorbance of (10ug/ml) on the same day. Inter-day precision was determined by checking the absorbance of (10ug/ml) on three different days. The %RSD was found to be 0.74% for intra-day and 0.95% inter-day as shown n table 2.

Table 2: Precision parameter for valsartan

Scans	Intra-day	Inter-day
1	1.0824	1.1023
2	1.0676	1.1056
3	1.0525	1.1018
4	1.1015	1.1085
5	1.0414	1.0984
6	1.1004	1.0786
Mean	1.0743	1.0992
SD	0.018455	0.014566
% RSD	1.72	1.33

Accuracy

Accuracy study was conducted by spiking at three different concentration levels (80%, 100%, 120%). At each level samples were scanned and from the absorbance recovery percentage was determined and presented in table 3.

Table 3: Accuracy parameter for valsartan

Level of recovery	Amount added (mg)	Amount found (mg)	% Recovery	Mean recovery
80%	8	7.96	99.5	99.2%
100%	10	9.95	99.5
120%	12	11.84	98.6

Robustness

To determine robustness of the method two parameters (wavelength and diluent composition) were made slightly different from the selected wavelength and diluent composition. No significant difference was found in the absorbance and hence the proposed method was considered as robust which is shown in table 4.

Table 4: Robustness parameter for valsartan

Method parameters

Adjust-ed to

Average absorbance

S.D

%RSD

Wave length (248.21nm)

249

1.0952

0.017542

1.6017

Diluent composition

(50:50)

55:45

1.0867

0.016924

1.5573

Ruggedness:

The ruggedness of the developed method was checked by analysing the samples by different analysts at different days at similar operational condition. The statistical analysis showed no significant differences were observed between results obtained employing different analysts, given in table 5.

Table 5: Ruggedness parameter for valsartan

Analyst	Days	Average absorbance	S.D	% RSD
1	1	1.0655	0.018355	1.72
2	2	1.0825	0.014245	1.31
3	3	1.0286	0.016342	1.59

Limit of detection and Limit of quantification:

Limit of detection is the lowest amount of an analyte in a sample that can be detected, but not necessarily quantified, under the stated experimental conditions. Limit of quantification is the lowest amount of analyte in a sample that can be quantified under stated experimental conditions. The LOD and LOQ for valsartan was found to be 0.15ug/ml, 0.45ug/ml.

Specificity:

A solution containing mixture of tablet excipients were prepared using the sample preparation procedure to evaluate the possible interference of the excipients. From the absorbance result no interference was observed from the excipients present in the formulation, indicated that the method is specific.

Assay of valsartan tablets:

Two different brands of valsartan were analysed using the validated method. For the analysis six replicates of each brand were assayed. 20 tablets of valsartan were weighed and finely powdered. An accurately weighed quantity of powder equivalent to 50mg of valsartan was taken in a 50ml volumetric flask. 10ml of methanol was added to it followed by 20ml of solvent. The solution was sonicated for 15 min and then filtered through whattmann filter paper (No. 41 ) and volume adjusted with the solvent. From this further dilution was made to get final concentration of 10ug/ml.

The results were presented in table 6.

Table 6: Assay for valsartan tablets

Sample

Label claim(mg)

Amount found(mg)

(± S.D)

% Amount found

Diovan

9.85±0.35

98.5

Valzaar

9.70±0.25

97.0

RESULTS AND DISCUSSION:

The method was validated and developed as per ICH guidelines. The method was validated in terms of linearity, precision, accuracy, robustness, ruggedness, LOD, LOQ and specificity. Beer’s law is obeyed over the concentration range of 2-20 µg/ml, using regression analysis the linear equation Y= 0.101x+0.009 with correlation coefficient of r² = 0.999. The precision results shows % RSD less than 2 at each level, which indicate clearly that the method is precise enough for the analysis of valsartan.The accuracy of the method was checked by recovery studies. The high recovery with values indicated the accuracy of the developed method. The robustness and ruggedness studies reveals that the method is enough robust and rugged. The LOD and LOQ values indicate sensitivity of the method. There was no interference observed from the excipients present in the formulation, indicated that the method is specific. Determination of valsartan in tablet formulation of two brands showed, content of valsartan were very close to the labelled amount. The %RSD values in all the parameters were within the acceptable limit.The optical characteristics of the method are represented in the

table 7.

Table 7: Optical characteristics of the proposed developed method.

Parameter	Value
λ_max	248.21nm
Beer’s range	2-20µg/ml
Correlation coefficient(r²)	0.999
Regression equation	Y= 0.101x+0.009
Intercept (C)	0.009
Slope (m)	0.101
(LOD µg/ml)&LOQ(µg/ml)	0.15 & 0.45
Precision (%RSD)	1.33

CONCLUSION:

A validated UV Spectrophotometric method has been developed for the estimation of valsartan in bulk as well as pharmaceutical dosage form. The developed method was found to be simple, accurate, précise, specific, reproducible and linear over the concentration range studied. The proposed method can be used for routine analysis of valsartan in bulk as well as pharmaceutical formulations.

ACKNOWLEDGEMENT:

The authors are thank full to Ranbaxy laboratories, Gurgaon, India for the providing the gift sample of valsartan for research work. We are thankful to the principal and management, maharajah’s college of pharmacy, Vizianagaram, for providing necessary facilities to carry out this research work.

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Received on 15.05.2016 Accepted on 02.07.2016

Asian J. Pharm. Ana. 2016; 6(3):147-150.

DOI: 10.5958/2231-5675.2016.00023.5